This invention relates to viscoelastic, shock-attenuating polyurethane elastomers and foams and to their preparation.
Polyurethanes and other types of elastomers and foams are being used extensively in many kinds of safety padding, e.g., knee protectors for contact sports such as wrestling, protective knee, shoulder and arm pads for football and soccer players, ice hockey and basketball players, and the like. Conventional polyurethane foams and elastomers currently in use for these applications are intended to perform the functions of load distribution and energy attenuation or absorption. Experimental and practical evidence shows that although such foams and elastomers are good load distributors, they are frequently deficient in their shock and energy-attenuating capabilities. Ball rebound and pendulum impact test data for many of these foams and elastomers reveal that they possess fairly high rebound velocity due to their relatively low hysteresis. Moreover, they exhibit high-peak deceleration and severity index. Neither of these properties are conducive to their functioning as good energy-attenuating polymeric substances.
In the field of footwear, insoles, outsoles, and other footwear components exhibiting energy-moderating or attenuating properties have been known for some time. Semi-flexible urethane foams have been used extensively in automotive interior safety padding such as crash pads, sun visors, arm rests, door panels, steering wheel panels, and the like. Stiffer semi-flexible foams and elastomers have been used in exterior safety applications, in particular, as shock-attenuating bumpers.
However, most of the products utilized by the automotive and footwear manufacturers exhibit relatively low hysteresis which is detrimental to good energy-attenuation. Other approaches have taken the form of a combination of a polyurethane exterior deformable front-pad backed by a relatively complicated hydraulic shock absorption system as, for example, represented by the newer automotive bumpers. Such approaches are not desirable from an economic point of view.
Attempts have been made to modify polyurethane foams and elastomers to obtain materials which possess more efficient energy-attenuating properties. U.S. Pat. No. 4,209,593 describes semi-flexible shock-absorbing polyurethane foams prepared from a polyether triol, a compound having a single reactive hydrogen, an aromatic polyisocyanate, blowing agent, chain extender and a catalyst. While these materials exhibit good shock-absorbing properties, the single reactive hydrogen reactant which is a naphthol, naphtholamine or a hydroabietyl alcohol imparts the undesirable characteristic odor of these aromatic compounds to the resulting foam. Other single reactive hydrogen reactants described in this patent are known carcinogens. Accordingly, this approach to shock-absorbing polyurethanes is not particularly desirable.
U.S. Pat. Nos. 4,346,205 and 4,476,258 are said to provide energy absorbing polyurethane foam and elastomer compositions having densities of 0.40 to 1.34 gm/cc. An attempt to repeat the examples of these two patents has revealed them to be inoperative since they only yield liquid materials which cannot be employed for the purposes intended. Other experiments within the broader disclosure of these patents have also resulted only in liquid materials. Such liquid materials are not useful for the purposes stated in these patents.
U.S. Pat. No. 4,230,168 describes the manufacture of high resiliency tire filling compounds from polyether polyols having equivalent weights from 900 to 1800, and polyisocyanates at isocyanate indexes of 0.8 to 2.0. The resulting polyurethanes exhibit very high rebound resiliency and are not suitable as energy-moderating polymers.